Weight and its impact on Fertility Treatment

The British Medical Association defines Body Mass Index (BMI) of 25-30 as overweight and BMI of 30-35 as obese. In the past 50 years, changes in lifestyle has led to an increase in weight in the general population bringing with it inherent health and other issues.

Overweight and obesity have been demonstrated to substantially reduce fertility in the general population. For those seeking to conceive through Assisted Reproductive Techniques (ART), its negative impact is evident at each stage of the treatment cycle.


The first complication is polycystic ovary syndrome (PCOS). This is a hormonal condition and affects 1 in 7 women of reproductive age. The frequency of PCOS increases significantly with obesity, and accounts for 30% of infertility cases in couples who seek treatment, conversely 80% of patients with PCOS who seek treatment are obese. Among other things PCOS may cause irregular menstrual cycles, absence of ovulation, which may in itself be the cause of infertility, and increase in hormonal and metabolic problems that affect fertility.

Quality of egg

Women are born with all the eggs they’ll ever have, and with age, both the quantity and the quality of those eggs decline. Menopause may not happen until the early 50s, but for most women, fertility begins to decline sharply around age 35. By age 40, a woman’s chance of getting pregnant is less than 5% per menstrual cycle, meaning fewer than 5 out of 100 women are expected to be successful each month they try.

Research suggests that excess weight, is one of the many factors that negatively affects the quality of egg, which further reduces the chances of a successful pregnancy even with IVF.

Ovulation induction and Medication

Women who are obese tend to respond poorly to ovulation induction, in some instances they may not ovulate at all, and need higher doses of medication in order achieve ovulation, the eggs produced have a higher risk of being immature, they also face a higher risk of cycle cancellation due to poor ovarian response.

In one study, the outcome of IUI treatment showed significantly lower peak oestradiol levels (this is the hormone that triggers the release of egg from its follicle) requiring higher doses and longer duration of medication, fewer oocytes (eggs) were retrieved and thus fewer total embryos harvested and subsequently, lower rate of fertilization.

Spontaneous abortion

Further, with fertilization rates being lower, the quality of embryo is lower and there are higher miscarriage rates.
Studies have further shown greater increase of immature oocytes and the chance of getting pregnant with a BMI over 30 was reduced by 25% while the risk of miscarriage was almost doubled and live birth rate was lower.
Whilst the presence of PCOS in women undergoing ART increased the risk of spontaneous abortion.

There are studies that suggest that the rate of embryo implantation, the chances that an embryo that’s put back into the body will stick, are less, and women with excess weight are 10 percent less likely to give birth to a live baby following IVF than women of average weight.

Pregnancy related complications

They are also at higher risk for pregnancy-related complications, including higher risk of miscarriage, hypertension, preterm birth, preeclampsia, and gestational diabetes.
Additionally, they face a high risk of surgical complications arising from reactions to anaesthesia if surgery is required, and postoperative complications thereafter.

IVF cut off point

Clinics have a duty of care towards their patients and will work towards achieving best outcomes for their patient’s treatment. They will not desire to put their patients unnecessarily through a traumatic experience and expensive procedure when they deem a successful outcome to be unlikely. They have therefore, a funding and treatment criteria in place in relation to weight.

Clinics are concerned with best outcomes for their patients and will always put patient’s health and emotional wellbeing at the forefront of any treatment, and to this end they have in place a BMI cut off of 35 for those undergoing private treatment.

NHS funding criteria is slightly more stringent, with a BMI cut off of 29.5. This however should not stop patients from seeking treatment and working with their practitioners to adopt healthy lifestyles to bring their BMI within acceptable levels in order to achieve desired outcomes.
Available data suggest that weight loss of as little as 5% – 10% can improve fertility outcome.

Positive way forward

Obesity is not an irreversible condition, and weight loss can be achieved through lifestyle modification, introduction of healthy diet and exercise. Which may induce enhanced reproductive function and improved response to fertility treatment, sustaining the weight loss would be critical for reduced complications during pregnancy and birth.
Rapid weight loss achieved through crash diets are not recommended as they prove detrimental to fertility treatment.


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